RuntimeError: Task attached to a different loop

Root cause

Background dispatcher queue and worker task were initialized from a session-scoped FastAPI app fixture before pytest-asyncio reset the event loop for the individual test, so the request handler awaited a Future bound to the stale loop.

Minimal fix

Change the FastAPI app/client fixtures to function scope, create dispatcher background tasks during awaited app startup inside the active pytest event loop, and ensure shutdown cancels/awaits workers before the loop is torn down.